1. Field of the Invention
The present invention relates to an ultraviolet (UV) sensor and a fabrication method thereof, and more particularly to a UV sensor including at least a silicon-rich (Si-rich) dielectric material and a fabrication method thereof.
2. Description of the Prior Art
The UV sensors (UVS) have been widely applied in fire hazard monitoring, contamination analyses, astronomical observations, medical facilities, and even military applications. Nowadays, UV sensors are further applied with light emitting diodes with material of Indium Gallium Nitride (InGaN) for example or laser device to form an ultraviolet-blue ray data access system.
In another aspect, the ozone layer in the atmosphere has long been damaged by chloroflurocarbons (CFCs) emitted by human related activities or other factors, causing the UV radiation near the surface of the earth to increase every year. Meanwhile, long term exposure under the UV light rays may cause pathological changes to human skins. Therefore, if a UV sensor could monitor UV levels, warnings of dangerous UV levels could be made in advance. For instance, the warnings provided by the UV sensor could warn the people immediately so that they can avoid going outside to be exposed to strong UV light rays or prepare with protection against the UV light rays.
In general, UV light rays are categorized into UV-A, UV-B, and UV-C. The UV-A, UV-B, and UV-C have wavelengths of 315 to 400 nanometers, 280 to 315 nanometers and 100 to 280 nanometers respectively. Of all three categories, UV-C with the shortest wavelengths has the most harmful radiation against the human beings. Fortunately, it is difficult for UV-C radiation to reach the Earth's surface. As a result, the primary sensing targets of UV sensors usually focus on UV-A and the UV-B.
Conventional UV sensors often use group III-V metals such as gallium nitride (GaN) or aluminum gallium nitride (AlGaN) as light sensing materials; however, these materials are often expensive such that the fabrication cost of the UV sensors cannot be effectively reduced. Also, the UV sensors with GaN or AlGaN materials as light sensing materials possess the issues of heavy contaminations as well as having difficulties to be integrated with semiconductor fabrication process. Moreover, the UV sensors with GaN or AlGaN materials also possess issues such as over heating of parts during sensing operation, which reduces the sensing performance, making these sensors impractical. In addition, amorphous silicon thin films or polycrystalline silicon thin films has been conventionally used as the light sensing materials of visible light sensor when integrating photosensor with a display panel; however, the amorphous silicon or the polycrystalline silicon materials are more sensitive to visible light and infrared light rays than UV light rays, and the amorphous silicon and polycrystalline silicon have poor photoelectric conversions as well as poor reliability. Therefore the amorphous silicon and the polycrystalline silicon materials cannot be applied in UV sensor products effectively. To summarize, the industry must continue in research to seek for the appropriate light sensing materials and structures for the UV sensors, and to provide a UV sensing structure and a fabrication method suitable for integrating the UV sensors to the semiconductor processes or display panels.